The present invention is related to crimped conjugate fibers and nonwoven fabrics produced therefrom.
Nonwoven fabrics are used in a variety of products such as sterilization wraps, medical drapes, disposable garments, diapers, protective covers, diapers and incontinence care products. Suitable nonwoven fabrics for such products need to provide desirable levels of softness, strength, durability, porosity, uniformity and other physical properties.
In an effort to improve desirable properties of nonwoven fabrics, multicomponent conjugate fiber nonwoven fabrics or webs have been developed. Methods for producing conjugate fiber nonwoven fabrics are disclosed, for example, in U.S. Pat. No. 3,423,266 to Davies et al.; U.S. Pat. No. 3,595,731 to Davies et al.; U.S. Pat. No. 5,108,820 to Kaneko et al. and U.S. Pat. No. 5,382,400 to Pike et al. A conjugate fiber nonwoven fabric is produced from polymeric fibers or filaments containing at least two polymeric component compositions that are arranged in substantially distinct sections across the cross-section along the length of the fibers or filaments. In general, useful properties, e.g., textural and functional properties, of such nonwoven fabrics can be improved by crimping the fibers of the nonwoven fabrics.
Crimped conjugate fibers can be produced by mechanically crimping fully formed conjugate fibers or, if the conjugate fibers have latent crimpability, by activating the latent crimpability. As is known in the art, such latent crimpability is imparted in conjugate fibers when the component polymers of the conjugate fibers are selected from different polymers having dissimilar shrinkage and/or crystallization properties, and such latent crimpability can be activated, for example, by a heat treatment that activates crimps, especially helically crimps, in the conjugate fibers.
Although, in general, imparting crimps in the fibers improves textural properties, e.g., softness and drapability, of a nonwoven fabric, the required level of crimps depends on each use of the nonwoven fabric. In addition, when conjugate fibers are overly crimped, the crimped fibers themselves tend to additionally form macro-crimps, forming randomly distributed clumped regions in the fibers. Such fiber clumps makes it highly difficult to produce a nonwoven fabric having a uniform fiber coverage and bulk. Consequently, it is important to have methods for controlling the level of crimps in conjugate fibers. In this regard, it is known that the level of crimps in the conjugate fibers can be controlled by producing conjugate fibers from different component polymers that have different shrinkage and/or crystallization properties, i.e., controlling the level of potential crimpability, and by varying the duration and temperature of the heat treatment, i.e., controlling the degree of crimp-activation. However, these known methods may not always be practical for different production set ups and when the component polymers of a conjugate fiber cannot be substituted with other polymers.
There remains a need for a production process that can be used to control the level of latent activatable crimps in conjugate fibers or filaments.